//对象转查询字符串
var page=1;
function objToSearchString(obj) {
    var str = '';
    for (var key in obj) {
        str += `${key}=${obj[key]}&`;
    }
    return str.slice(0, str.length - 1)
}

//封装ajax函数
function ajax(method, url, params,) {
    return new Promise((resolve,reject)=>{
    //创建一个实例化请求对象
    var xhr = new XMLHttpRequest()
    //配置请求对象
    xhr.open(method, method == 'get' ? url + '?' + objToSearchString(params) : url)
    //设置回调函数
    xhr.onreadystatechange = function () {
        if (xhr.readyState == 4) {
            resolve( JSON.parse(xhr.responseText ) );
        }
    }
    xhr.setRequestHeader('content-type', 'application/x-www-form-urlencoded');
    xhr.send(method == 'get' ? null : objToSearchString(params));
    })
    
}